Neandertal Human Issue

From: http://en.wikipedia.org/wiki/Talk:Anatomically_modern_humans#Homo_sapiens_articles -- discussion

The case for Neanderthals-Human barrier.

1. Neanderthals are now extinct, therefore tests for inter-fertility or future hybridization are not possible.
2. Humans and Neanderthals coexisted over the range of geographic barriers from Siberia to Iberia within the last glacial period up to < 26kya in Iberia, the initial contact between humans and Neanderthals began about 40kya and therefore they overlapped at least 14,000 years.
3. Human males tend not to have a problem exchanging gametes with other females from disperse populations when given a chance.
4. This would indicate we should see Neanderthal mtDNA within the European population, of course local population drops, such as might have occurred during the LGM in Iberia might have cause the loss. OTOH it appears currently that several mtDNA lines survived the LGM in Iberia. Along with HLA, and other genetic markers.
5. Therefore if Humans and Neanderthals mixed we expect to see a stronger signal of relationship in two areas which show strong West Atlantic relationships, Ireland and N. Iberia.
6. Paabo and Hublin have basically stated this is not the case. There is no evidence. If we assume that the population of Neanderthals and Humans in the region for the 14,000 (500+ generations) year period and that the populations of either was 3000 individuals then it approximates fertile hybrids were formed at a frequency of less than [single selection probability genomic detection limit]/1,000,000 limit matings or there was an infertility barrier. I would posit that it was an infertility barrier.

I have not seen their data from which they are making these claims, however they claim they have 60% of the N genome sequenced, some areas as many as 6 times. With these high hit areas, provided they have done adequate chimpanzee on gorilla sequence for the same areas they should be able to determine sites derived in human and not in Neanderthal (the reverse derived in Neanderthal but not in human can be the result of sequencing errors). They should have sufficient enough information to place the low limit. They have sequenced however one Croatian which shows very close genetic relationship with most other European Neandertals. It does not rule out gene flow into Neandertals within Central Asia, however it appears to rule out gene flow from Neandertals into humans. We would have to know what they are using as their basis (HapMap for example) 7. If we are calling 'white' as intermixing and 'black' as a formal divide, then in terms of grey zones, the color is very close to, if not, 'black'.

Alternative hypothesis. 1. Hublin and Paabo show that inter-fertility may have continued to about 350ky. Morphological evidence in the form of Petralona appears to support gene flow from Africa after the establishment of the Sima de los Huecos population 600 kya (85% percent of what defines about Homo heidelbergensis comes from this cave system) the earliest find at Atapuerca cave system (in which SdlH is a part) is from 800 kya but its' origin (Africa versus Asia) is disputed. (Again I have not had a chance to see their data or go over it) 2. North Africa populations appear most similar to Bodo and Kabwe 1, which means it is either a 3rd species (formal) or an intermediate between Homo sapiens and Neandertals, such an intermediate cannot be excluded by their data if the rate of gene flow between region ends is less that 3000 miles per 350,000 years. This would match the arctic sea bird scenario where species in adjacent ranges can intermix but not species across the range. If the rate of admixture was low (~1/1000 matings at the boundaries) but not rare.

I think the evidence is unequivocal, either N/H boundary is formal in every sense, or that these two populations were biological species in most senses that science accepts as species. I refer everyone to this months Special Edition on Human origins in PNAS. There are contributions from both OoA supporters and those who have been against OoA, and I think the tide in the last year has changed in the direction of strictly OoA.

I lieu of the fact that I have not had a chance to go over sequence information presented by Paabo and company, that the matter is open as a consequence of the potential for error, which several groups claim the previous mostly-OoA claim was an error, but now corrected. There has to be a little caveot emptor.

   Neanderthal's were physically more powerful than AMH. Neanderthal men could have easily overpowered AMH and stolen their women and mated with them. So the presence of Neanderthal Y-DNA is also a possibility. Wapondaponda (talk) 17:59, 24 September 2009 (UTC)

       I'm all for imaginative fiction but this is not the place to exercise such talents. You are making up a story that may or may not be true.--Andrew Lancaster (talk) 22:09, 24 September 2009 (UTC)

       There is nothing that can be interpreted from the TMRCA of Y chromosome, it expanded after the fact from the same place that mtDNA appear to have first split. So either it randomly re-expanded from S.Africa (and if could have come from anywhere) or the molecular clocking is way off. I have focused on what we know about mtDNA and X-linked, I will leave it up to for future gene-jockey's to clear up what is going on with Y chromosome. Lets say that the TMRCA for Y is 50 kya, and humans and Neanderthals last made contact 30 kya, Y could have subsequently spread into Europe after this period and replaced all previous Y, human or Neanderthal without discrimination. If there was a species barrier between the two (And I would say the likelihood was very high) then we simply do not know what it is, and moreover we do not know the attraction/mating biology or rituals of the Neanderthal, they may have had neither estrus or menstruation, and the cues of human males to neanderthal females and vice versa may have been repulsive, not attractive. In a sense speculation on this is worthless because we have no clues in any direction.PB666 yap 05:00, 25 September 2009 (UTC)

           I just wanted to point out that interbreeding doesn't only mean AMH men and Neanderthal Women, it could also mean Neanderthal men and AMH women. Neanderthals had robust skeletons on which large muscles were attached. So it is interesting question as to why the physically stronger species went extinct. Though the two species have a distinct morphology, the morphologies were still similar enough that some individuals from each species would have found each other attractive. Given the diversity of human fetishes, there isn't much doubt that mating was attempted over the 20,000 years that the range of the two species overlapped. Given the fairly recent divergence between the two species, conception would have been a possibility, however complications could have resulted in frequent miscarriage. This is the hypothesis by
           Shlain (2004). Sex, time, and power: how women's sexuality shaped human evolution. ISBN 0142004677. http://books.google.com/books?id=FvKyJqiX_XwC&pg=PA3#v=onepage&q=&f=false.

           The hypothesis suggests homo sapiens went through a major bottleneck prior to speciation that would have significantly altered gene frequencies from ancestral archaic populations. Homo Sapiens have tiny pelvis that causes major complications at birth, solving that problem 200kya was a major event in human history. Neanderthals also appear to have underwent a severe bottleneck as they endured several ice-ages. These two events could have accelerated the divergence between the two species leading to a fertility barrier. Wapondaponda (talk) 07:16, 25 September 2009 (UTC)

               I don't know that any of that is true. Neandertals, and many late Archaics had equally massive brain cases. The brain cases of robust individuals at birth is thicker and less plyable that those of gracile individuals. In the case of Skhul V and some Neandertals you are dealing with infants who had larger brains, more robust skulls,etc. The other thing, AMH-Homo sapiens may have by and large entered a speciation event in within SSA that excluded the parent species and other species in Africa, these things we do not yet know.PB666 yap 21:42, 25 September 2009 (UTC)